The present invention relates generally to a self-monitor system for a microprocessor which generates an alarm when an IC package constituting the microprocessor is erroneously connected to a printed circuit board. More specifically, the invention relates to a microprocessor which can perform a self-check during so-called "cold start" confirming accurate connection of the IC package to the printed circuit board.
In general, the IC package of a microprocessor is connected to a printed circuit board by inserting a plurality of terminals thereof into connector openings of an IC connector socket. The pins of the IC package are arranged in alignment along parallel edges of the base of the IC in the so-called "dual in-line" package arrangement. The IC socket has a plurality of connector openings arranged to match the positions of the IC terminal pins.
It is possible to connect the IC package to the printed circuit board with the IC package reversed so that the pin order is reversed in the socket. In order to prevent this, positioning markers are provided on both the IC package and the IC socket. Although erroneous insertion can be avoided to a large extent by applying such positioning markers, this cannot completely eliminate erroneous insertions due to inadvertent errors of workers. Once the IC package has been erroneously inserted into the IC socket of the printed circuit board, it becomes very difficult to uncover erroneously connected IC packages.
Another common problem concerns more complex systems in which several different IC's are installed to perform a variety of functions. In this case, it is easy to confuse IC packages which are externally identical but which are uniquely programmed for different operations. Thus, for example, a microprocessor IC intended for use in an anti-skid control system might inadvertedly be installed in an IC socket wired into an air conditioning control circuit, and vice versa.